The present invention relates to magnetic disk subsystems and more particularly to means for compressively securing a stack of axially aligned magnetic disks, while assuring that the endmost ones of the disks remain flat and normal to the axis of the pack.
In digital information systems, it is necessary that a vast number of digital bits be stored for subsequent use by data processing circuitry. Although different approaches, such as optical, electrostatic, and electronic, have been used with varying degrees of success as memory units the vast majority of present-day information systems make use of magnetizable elements for storing the digital information. Arrays of magnetizable cores wired in matrices have been widely used, although with the increasing amount of data to be stored and retrieved it has been found desirable to use a translatable medium such as magnetic drums, tape or disks. While tape has found considerable favor, it is necessary to dispose most information on tape in serial fashion. Thus, although a given length of tape may be provided with several parallel tracks, for any given track it is necessary to reel or unreel a length of tape to arrive at a position where a predetermined item of information is stored.
For these and other reasons it has been found advantageous to store digital information upon groups of magnetic disks. In the present context, the term "magnetic disk" is used to denote a circular, planar element having a magnetizable surface. By stacking numbers of disks together in axially spaced relationship, upon a rotatable spindle, it is possible to access numbers of disks at the same time; or, to switch electronically from a transducer adjacent one disk to a similar, parallel transducer which is in contact with a different disk. Thus, a numer of different "addresses" may be accessed in parallel fashion, without the need for traversing many intermediate locations.
An advanced approach to the foregoing method of providing data is disclosed in U.S. Pat. Nos. 3,864,750 and 3,864,747 in which multiple stacks of magnetic disks are driven in synchronism by a common drive means, and accessed by means of an access mechanism having a plurality of magnetic heads, one for each disk surface.
Obviously, economy demands that as many disks as possible be placed in a single stack to avoid the unnecessary duplication of drive and access means. Further, with the introduction of larger disk packs which are non-removable, the number of disk surfaces per stack has been substantially increased. Accordingly, it will be seen that it is desirable to be able to stack as many disks as possible upon a given spindle for simultaneous access by a set of magnetic heads.
Aside from the mechanical constraints which limit the size and weight of a given disk pack, an additional problem arises with the increasing density of data bits per unit area which are written upon the disks. As the bit density increases, the dimensional accuracy of the disk surfaces and transducer heads has become even more important. Also, the accurate tracking of the heads over the disk surfaces has become critical to the operation of the system.
It has been found that the previously-used methods for clamping disks in an axial stack are inadequate to satisfy the increased dimensional requirements. In particular, it has been found that the endmost ones of the disks, which bear the brunt of the initial clamping forces, tend to dish outwardly from the stack. Although this phenomenon has been noted, to date its solution has eluded those skilled in the art. In fact, in many commercial units presently being offered for sale the endmost ones of the disks are considered sacrificial, and are not used for storing digital information due to he above-described distortion.
Accordingly, it will be appreciated that it would be advantageous to provide a means and method for transmitting clamping forces to a stack of magnetic memory disks which allow the endmost ones of the disks to remain substantially parallel, enabling them to be used for storing data.
it is therefore an object of the present invention to provide improved means for applying clamping forces to a stack of magnetic disks.
It is another object of the invention to provide an improved method for clamping a plurality of magnetic disks together to form an axially-aligned stack.
Another object of the invention is to provide clamping means for applying pressure to an axially-aligned group of magnetic disks which does not effect a significant dishing of the endmost ones of the disks.